Brake proportioning means



June 30, 1970 M. CRIPE 3,517,

BRAKE PROPORTIONING MEANS Filed Nov. 4, 1968 FRONT BRAKES I 26 54 w 22I2 5 [4 I6 REAR BRAKES 2;; 64 H6 3 30 33 I20 62 n 132 I /00 7 92 9. 94

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72 //.Z MAXWELL LCEIPE' 3 /06 //0 W05 @MQ/g yak ATTOENE Y United StatesPatent 3,517,970 BRAKE PROPORTIONING MEANS Maxwell L. Cripe, South Bend,Ind., assignor to The Bendix Corporation, a corporation of DelawareFiled Nov. 4, 1968, Ser. No. 773,074 Int. Cl. B60t 8/26 US. Cl. 303-6 2Claims ABSTRACT OF THE DISCLOSURE A proportioning means for a dualhydraulic brake system that will regulate the brake pressure in oneportion of that system in two steps by utilizing a device responsive toa control pressure for proportioning the brake pressure in steps.

SUMMARY As may be realized by those skilled in the art to which thisinvention relates vehicle brake design for many years now has attempteda reasonable compromise between rear brake effort and front brake effortin accordance with the design of the wheel cylinders for the rear wheelbrakes and the front wheel brakes. Of late there have been attempts toutilize similar wheel cylinders in both the front and rear brakes byproviding a brake proportioning means adapted to reduce brake pressurein the rear wheel brakes based upon a predetermined inlet pressurecorresponding to front wheel brake pressure that takes effect upon theweight shift during a deceleration to antomatically proportion the rearhydraulic brake pressure as a function of front hydraulic brakepressure.

Most of the prior art designs to proportion braking pressure have simplyutilized input pressure from the master cylinder as the reference sourcefor regulating the output pressure to the rear wheel brakes, generallyspeaking. However, there have been some attempts recently to moreidealize the pressure relationship of front and rear wheel brakes byincorporating elements to render the brake proportioning device moreresponsive to the shift in weight. These devices have involved simplebut yet additional structure linking the brake proportioning devicebetween the vehicle and the rear axle in order to utilize the increaseddistance due to a weight shi'ft therebetween as the load shift input tothe valving mechanism. The attempt here was to more readily maintain therelationship of the rear brake pressure to input pressure, or frontwheel pressure, within the span of the curves for such relationship onthat vehicle when it is empty and when it is loaded. There can be nodoubt that a better balanced vehicle brake system is provided by suchload sensitive devices. On the other hand, it is equally true that theseprior art devices still provided a straight line curve stepped at apoint to maintain it under the ideal curvilinear function of the rearbrake pressure to front brake pressure desired.

It is, therefore, a principal object of this invention to provide abrake pressure proportioning device which will utilize a controlpressure for providing a multi stepped relationship of rear brakepressures to front brake pressures that will more readily approach theideal curvilinear relationship without crossing thereover in all rangesof the vehicle loading.

It is another object of this invention to provide a brake proportioningdevice in a brake system utilizing a servomotor operated master cylinderby tapping the control pressure for the servomotor and providing it to aslave servomotor and hydraulic cylinder, which hydraulic cylinder isinterposed in the brake system between a portion of the split mastercylinder and the rear wheel brake actuator, such that the controlpressure will regulate a 'ice piston valve in the proportioningmechanism by means of walls whose rate of movement is controlled byspring means of different values of force.

DRAWING DESCRIPTION Other objects and advantages will appear from thefollowing description of the drawing in which there is shown a vehiclebrake system employing a servomotor operated master cylinder with abrake proportioning device in accordance with the principles of thisinvention shown in cross section to be interposed between a portion ofthe split master cylinder and a brake actuator, more particularly, therear wheel brake actuating means.

DETAILED DESCRIPTION With more particular reference to the figure, thereis shown a vacuum over air servomotor 10, such as is familiar to thoseskilled in the art that is aifixed by bolts 12 to a firewall to beoperated by a brake pedal 14 within the operators compartment of thevehicle. The servomotor 10 has bolted thereto a master cylinder 16 withseparate discharge ports 18 and 20 to which conduits 22 and 24 arejoined.

Conduit 22 leads to a caliper type disc brake motor 26 for the frontwheel brakes of the vehicle; whereas conduit 24 leads to an inlet 28 ofa slave cylinder 30 that has an outlet port 32 connected to a caliperdisc brake motor 34 of the rear wheel brakes.

The vacuum over air servomotor receives vacuum via a check valve 36connected by conduits 38 to the vehicles engine intake manifold 40,which conduit 38 is provided with a branch 42 connected to an inlet port44 for a slave motor housing 46 to which slave cylinder 30' is affixedby bolts 48.

As has been indicated, the servomotor 10 is of a conventional type, andit will be, therefore, readily recognized that it has a control chamberand a reference pressure chamber with the latter in open communicationvia the check valve 36 to the vacuum of the engine intake manifold 40.Normally the control chamber and the reference pressure chamber arecommunicated by an internal passage arrangement and valve means within amovable wall of the servomotor 10 that is closed upon depressing brakepedal 14 whereby atmospheric air entering at the end of the boot 50 isintroduced to the servomotor control chamber. With this invention inmind, a conduit 52 is affixed to the rear shell 54 of servomotor 10 soas to be opened to the control chamber thereof and thereby providingmeans of conduction of the controlled chamber pressure to an inlet port56 of the slave servomotor housing 46.

As can be readily visualized the slave servomotor housing 46 iscomprised of a plurality of sections which are joinedtogether by boltmeans (not shown) and the juncture of the various section are sealed byperipheral portions 58 and 60 of diaphragms 62 and 64. The intermediatesection is provided with a partition 66 of annular design and provisionto mount the seal 68 in the central opening thereof. Diaphragm 64 isassemblable to a force transmitting rod 70 by means of plates 72 and 74held against a shoulder 76 of rod 70 by a nut 78. Diaphragm 62, on theother hand, is supported by means of a plate 80 being held by a nut 82to an annular plate 84 having forwardly and rearwardly extending bosses86 and 88, the former of which mounts a seal means 90 and the latter ofwhich is externally threaded for receipt of nut 82 and provided with abore slidably receiving tubular end 92 of rod 7-0. The tubular end 92 ofthe rod 70 is provided with transverse openings 94 so that chamber 96opens to port 44 can be communicated to chamber 98 via the tubular end92. A snap ring 100 is affixed to the tubular end 92 to provide anabutment surface for the boss 88 of the plate 84 supporting diaphragm 62that connects the diaphragm 62 and its plates which form a movable wallassembly to the push rod 70 when the aforesaid movable wall assemblymoves to the left as viewed in the figure. Upon assembly a light spring102 is inserted to be between partition 66 and plate 72 of the movablewall assembly formed by diaphragm 64 and plate 72, 74; whereas a heavyspring 104 is placed between the end of the housing and the movable wallassembly comprised of diaphragm 62 and plates 80, 84. The intermediateand forward sections of housing 46 are provided with aligned passages106 and 108 that upon assembly communicate, via an opening 110 in theperipheral portion of diaphragm 64-, chamber 112 open to port 56 tochamber 114.

Within the slave cylinder 30 connected to housing 46 by bolts 48 priorto the assembly of the movable wall means therein, a seal structure 116closes the leftward end of a stepped bore 118 for housing 30 and a plug120 is held by a snap ring (not shown) closes the other end of thestepped bore. A combination seal retainer and spring bearing means 122locates the seal 116 and supports a spring 124 at one end, whose otherend is bearing on an annular piston 126 between inlet chamber 128 andoutlet chamber 130- of the slave cylinder 30. Rod 70 extends through theannular piston 126 and terminates in a threaded portion 132, to which isassembled so as to face a valve seat 131 for piston 126 a poppet valve134, having a forwardly projecting boss 136 cooperating with plug 120 toform a stop prescribing the rest position of the movable wall assemblieswithin housing 46 and the spacing between valve 134 and valve seat 131of piston 126 in view of stop ring 138 being normally abutting shoulder140 of stepped bore 118 under the action of spring 124.

OPERATION In operation the vehicle operator will depress brake pedal 14to introduce atmospheric control pressure into control chamber forservomotor to create a differential pressure across the movable wallthereof and thereby develop hydraulic pressure in conduits 22 and 24. Atfirst the hydraulic pressure is communicated to both the motors 26 and34 in that spring 102 is strong enough to maintain the position of rod70 as shown in the figure. However, as control pressure builds withinthe servomotor 10, it also builds within chambers 112 and 114 toeventually overcome spring 102 and close poppet 134 on seat 131 toterminate the communication of hydraulic pressure from conduit 24 to thedisc brake motor 34. If the vehicle operator is still scheduling furtherbraking effort and increasing the hydraulic pressure by applying morecontrol pressure in the servomotor 10, the movable wall assemblycomprised of diaphragm 64 and plate 74 will move to a position to reducethe rate of increase of hydraulic pressure for the rear brake system.Eventually control pressure will reach a magnitude which will start thecompression of the spring 104 to provide additional force on the rod 70-for further stepping down the rear brake pressure. However, it should berealized that the movable wall assembly comprised of diaphragm 62 and 4plates 82, 84 will not be effective until at the point of run-out of themovable wall assembly comprised of diaphragm 64 and plates 72, 74.

Upon release of the brakes the reintroduction of vacuum into the controlchamber for the servomotor 10 will reintroduce vacuum to chamber 112 and114 permitting springs 104 and 102 to return the diaphragms 62 and 64 totheir rest position, as shown in the figure. Spring 102 will also urgethe movement of the poppet valve 134 to separate from the valve seat 131which is assisted in that the inlet pressure via conduit 24 has beenreleased so that the pressure within the brake system from the actuator34 back to the slave cylinder will cause piston 126 to maintain thespacing of the poppet 1.34 from seat 131. This provides a proportioningsystem with a low hysteresis during release which is a desirableattribute.

Having fully described an operative manner of construction for thisinvention, it is now desired to set forth the intended protection soughtby these Letters Patent in the appended claims.

I claim:

1. In a hydraulic brake system a means to proportion rear brakepressure, said means comprising:

an operator-operated fluid pressure servomotor;

a split master cylinder connected to said servomotor to develop separatebrake pressures for separate brake actuators; and

a proportioning means having a slave servomotor connected by conduitmeans to control pressure for said operator-operated servomotor and to areference pressure source also connected to said operatoroperatedservomotor, said proportioning means also having a slave cylinderinterposd between said master cylinder and one of said brake actuatorsfor one of said separate brake pressures, at least, which slave cylinderhas piston valve means controlled by said slave servomotor to controlcommunication of said master cylinder and brake actuator and controlsystem displacement between said slave cylinder and said actuator in avarying proportion tosaid control pressure.

2. The structure of claim 1 and further characterized in that said slaveservomotor has at least two movable walls biased by separate spings ofdiffering force value to bring about the varying proportion of slavecylinder pressure to control pressure.

References Cited UNITED STATES PATENTS 3,201,176 8/1965 Hager -545 X3,201,177 8/1965 Cripe 3036 3,245,726 4/1966 Stelzer 30'36 MILTONBUCHLER, Primary Examiner J. J. McLAUGHLIN, JR., Assistant Examiner US.01. X.R.

